1. Field of the Invention
This invention relates to a molded conveyor chain having number of link plates of synthetic resin pivotally connected together by connecting pine and driven by sprockets for conveyance of delicate or easy-to-break articles in the electric, electronic, food-processing or pharmaceutical industry.
2. Prior Art
Various molded conveyor chains having a number of link plates of synthetic resin connected together by connecting pins are known. As shown in FIG. 11, the connecting pins of the conventional molded conveyor chains have a flat portion 51 on its circumferential surface, and two projections 52, 52 formed on the flat portion 51 at positions equidistant from the center of the connecting pin 50. Tn the assembled Plate of the conveyor chain as shown in FIG. 12, a barrel end of one link plate 60 and an open end of the adjacent link plate 60 are pivotally connected by one of the connecting pins 50. Each of the projections 52, 52 of the connecting pin 50 has an outer edge engaged with an inner surface of one of two hinges at the open end of the link plate 60, and opposite end portions of the connecting pin 50 are located inside two aligned pin holes 61, 61 of the hinges of the link plate 60. The connecting pin 50 is received in a bush hole 62 formed in a hinge at the barrel end of the link plate 60 with a clearance therebetween. Sliding engagement between the circumferential surface of the connecting pin 50 and the bush hole 62 in the link plate 60 enables the conveyor chain to bend or flex about the axis of the connecting pin 50.
The illustrated conventional molded conveyor chain has various drawbacks as enumerated below.
(1) The opposite end portions of the connecting pin 50 have a length Y set to be smaller than the width X of each hinge of the link plate 60, as shown in FIG. 12. Accordingly, when the operator attempts to insert the connecting pin 50 alternately into the pin holes 61 and the bush hole 62 to pivotally connect two adjacent link plates 60, 60, the forward movement of the connecting pin 50 is arrested when a loading one of the projections 52 comes into engagement with an outer surface of one of the hinges of one link plate 60. To cope with this problem, the operator is forced to hammer the trailing end of the connecting pin 50 while gripping the two link plates in such a manner as to maintain accurate alignment between the pin holes and the bush hole. Such link-plate joining operation is tedious and time consuming and exerts a great load on the operator. Furthermore, when the two link plates 60 are to be detached, the connecting pin 50 is axially driven with a hammer until two projections 52 move past the pin hole 61 which is located at the open end of the link plate 50. This means that a stroke Z of hammering the connecting pin 50 to remove the connecting pin 50 from the two adjacent link plates 60, 60 is substantially equal to the length of the connecting pin 50. Such a large hammering stroke considerably lowers the efficiency of the link-plate detaching. A conveyor chain disassembling work also encounter with the same problem because this work involves the connecting pin detaching operation.
(2) In the case where the conveyor chain is automatically assembled on a special automatic assembling machine, the positions of the projections 52, 52 on each connecting pin 50 are precisely controlled in such a manner that the projections 52 are in engagement with the opposed inner surfaces of two hinges of each link plate 60. It may occur, however, that when opposite ends of the conveyor chain are manually joined together to set the conveyor chain on a conveyor frame, the connecting pin 50 is driven either excessively or insufficiently. In this instance, one of the projections 52 of the connecting pin 50 is caught or arrested within a corresponding one of the pin holes 61 of the link plate 60. Due to a stress exerted from the projection 52 to the peripheral wall of the pin hole 61, the hinge having the thus stressed connecting pin hole tends to break while the conveyor chain is running. This will cause a downtime of the conveyor chain.